The present invention relates to a production process for an ethylenimine polymer aqueous solution.
An ethylenimine polymer is obtained by polymerizing ethylenimine in the presence of a polymerization initiator, and the resulting ethylenimine polymer has a low polymerization degree in polymerization in the absence of a solvent because of a problem on a viscosity. Accordingly, polymerization reaction is carried out in a water based medium in order to obtain an ethylenimine polymer having a high polymerization degree to obtain the ethylenimine polymer having a high molecular weight in the form of an aqueous solution thereof. Described in, for example, Japanese Patent Publication No. 8828/1968 is a process in which ethylenimine is polymerized in a water based solution at a temperature falling in a range of 50xc2x0 C. to a boiling point of the ethylenimine aqueous solution in the presence of a polyhaloalkane polymerization initiator to thereby obtain an ethylenimine polymer aqueous solution.
However, an ethylenimine polymer aqueous solution obtained by a conventional process has the problem that the viscosity is reduced with the passage of time, that is, the quality is not stabilized. Further, it has been difficult to produce an ethylenimine polymer aqueous solution having a high concentration (high resin content) by a conventional process.
Accordingly, an object of the present invention is to provide a production process for an ethylenimine polymer aqueous solution which has a high concentration and is less changeable with the passage of time, that is, has a stabilized quality.
The present inventors have found that the object described above can be achieved by polymerizing ethylenimine at a relatively low temperature and then ripening in a specific temperature range.
Thus, according to the present invention, provided is a process for polymerizing ethylenimine in a water based medium to produce an ethylenimine polymer aqueous solution, wherein ethylenimine is polymerized at a temperature of 80xc2x0 C. or lower and then ripened at a temperature of 100 to 150xc2x0 C.
Ethylenimine used as a raw material in the present invention shall not specifically be restricted. Capable of being used in the present invention is any of ethylenimines obtained by, for example, a process in which halogenated ethylamine is subjected to intermolecular cyclization with concentrated alkali, a process in which monoethanolamine sulfuric acid ester is subjected to intermolecular cyclization with hot concentrated alkali and a process in which monoethanolamine is subjected to catalytic vapor phase intermolecular dehydration reaction.
Compounds usually used for polymerization of ethylenimine can be used as the polymerization initiator, and suitably used are haloalkanes such as 1,2-dichloroethane, 1,3-dichloropropane, 1,2-dibromoethane and chloroform. A use amount of the polymerization initiator can suitably be selected depending on a molecular weight of the intended ethylenimine polymer. In order to obtain an aqueous solution of a high molecular weight ethylenimine polymer, it is suitably used in a proportion of 0.5 to 5% by weight based on ethylenimine.
Usually, water is used as the water based medium, but capable of being used as well are mixtures of water with water-soluble organic solvents such as methanol, ethanol, acetone and dimethylformamide.
In the present invention, ethylenimine is polymerized at a temperature of 80xc2x0 C. or lower, preferably 50 to 70xc2x0 C. The temperature exceeding 80xc2x0 C. can not provide an ethylenimine polymer aqueous solution having a stable quality. On the other hand, the too low temperature elongates the polymerization time and therefore is not economical.
In the present invention, the reaction solution is heated to 100 to 150xc2x0 C., preferably 110 to 140xc2x0 C. after polymerization of ethylenimine is finished, preferably after 95% or more of ethylenimine fed is consumed, and then it is ripened in this temperature range. The temperature lower than 100xc2x0 C. can not provide an ethylenimine polymer aqueous solution having a stable quality. On the other hand, the temperature higher than 150xc2x0 C. causes thermal decomposition of the resulting ethylenimine polymer, so that the polymer having a high molecular weight is not obtained in a certain case. The ripening time is usually 2 to 20 hours, preferably 4 to 10 hours. Also, time consumed for heating the reaction solution up to the ripening temperature is usually 0.2 to 5 hours, preferably 0.5 to 3 hours.
In polymerization reaction of ethylenimine in the present invention, the polymerization initiator and ethylenimine may be added in one lot, but because of exothermic reaction, it is recommendable to continuously feed each of them while controlling the temperature.
The polymerization reaction can be carried out under either atmospheric pressure or applied pressure. Usually, a pressure of 0 to 10 MPaG, preferably 0 to 2 MPaG is employed. It is recommendable to ripen the reaction solution usually under applying a pressure of 0.05 to 10 MPaG, preferably 0.05 to 1 MPaG.
The polymerization reaction and the ripening treatment can be carried out by any reaction form of a batch system, a semi-batch system and a continuous flow system. When carried out by the batch system, the polymer has an elevated viscosity particularly in polymerization reaction, so that suitably used is a stirring blade for a high viscosity for removing heat, dispersing and accelerating reaction, for example, a Max Blend blade (manufactured by Sumitomo Juki Ind. Co., Ltd.). In this case, a vertical shell and tube type condenser is preferably used in order to effectively remove heat to polymerize ethylenimine under refluxing.
The ethylenimine polymer aqueous solution obtained according to the process of the present invention has a concentration (resin content) of usually 20 to 70% by weight. Also, the ethylenimine polymer has an average molecular weight of 1,000 to 1,000,000 (determined by gel permeation chromatography (GPC); pluran-reduced).
The ethylenimine polymer aqueous solution obtained according to the process of the present invention is widely used in the fields such as a paper processing agent, an adhesive, a coating material, an ink, a fiber treating agent, a flocculant, cosmetics, toiletries and a dispersant.
According to the process of the present invention, obtained is an ethylenimine polymer aqueous solution which is less changeable with the passage of time and has a stabilized quality and which contains the ethylenimine polymer in a high concentration of 20 to 70 mass %.